The female staff member was in a corridor in the ape house when Vicky – a 24-year-old orang-utan – snapped.

She bit the keeper on the arm and foot. An ambulance was called to the East Park Drive attraction and took the injured woman to hospital for emergency treatment while fellow staff coaxed Vicky back into her den.

The keeper, who has worked for the zoo for five years, was kept in hospital for three days following the incident on Friday.

Jude Rothwell, communications manager at Blackpool Zoo, said: "At this point it is not known how the orang-utan gained access to the corridor.

"A full investigation into the incident is being carried out and all personnel involved have, or will be interviewed.

"At no point was the public in any danger.

"The orang-utan was confined to the staff access corridor, inside the ape house, where a series of safety doors prevent access to outside the exhibit.

"Blackpool Zoo has protocols and procedures for all aspects of its operation and has an exemplary safety record. This is an isolated incident and until the investigation is completed, Blackpool Zoo is unable to comment further."

She added: "The keeper is doing very well and making a good recovery. She is now out of hospital."

Blackpool Council, the investigating authority, said health and safety officers were now interviewing members of staff. A spokesman said: "We can confirm that the council is investigating an accident in Blackpool Zoo which resulted in a member of staff being injured."

Vicky has been popular with visitors since she was born at the zoo in 1984.

She was rejected at birth by her mother and had to be hand reared. The ape even appeared on TV when she learned how to blow her own nose after catching flu.

Last week's incident came five months after another investigation was launched into the death of another orang-utan – an eight-year-old called Beau found in a moat.